Method of making a plate microlens

Abstract

In a plate microlens of the invention, wherein gradient index lenses each having an optical axis along a normal to a surface of a transparent base and a refractive index profile gradually changing along a direction of the optical axis and a direction perpendicular thereto are formed integrally in the transparent base; a ratio d/a (where d is a thickness of the gradient index lens on the optical axis and 2a is a diameter of the gradient index lens on a surface of the transparent base) falls within a range of 0.46 to 0.78. In a method for manufacturing a plate microlens of the invention, of forming integrally in a transparent base, gradient index lenses with a gradient index profile based on a concentration gradient of a substance for increasing the refractive index of the transparent base, by forming a diffusion preventive mask with predetermined apertures on a surface of the transparent base and diffusing the substance into the transparent base through the apertures; a ratio a/rm (where rm is a radius of the apertures and a is a radius of the gradient index lenses to be formed) satisfies a relation 1.75≦a/rm≦4.5.

What is claimed is: 
     
       1. A method of making a plate microlens having a transparent base of glass containing SiO 2  of 45 to 80mol%, an alkali-metal oxide of 8 to 35 mol%, ZnO of 2 to 20 mol%, B 2  O 3  of 0 to 8 mol%, Al 2  O 3  of 0 to 7 mol%, ZrO 2  of 0 to 2 mol%, and CaO+BaO+MgO of 0 to 10 mol%, the base having a substantially planar surface and the base also having a plurality of gradient index lenses formed within the base and each lens having an optical axis normal to the planar surface of the base, a substantially circular cross section along the planar surface, and a refractive index profile gradually changing along the respective optical axis and each lens having a ratio d/a of 0.46 to 0.78 where d is the axial thickness of the respective gradient index lens along its optical axis and a is half the diametral width of the respective gradient index lens measured along the planar surface of the base, the diametral width being perpendicular to the respective optical axis, the method comprising the steps of: a) providing the transparent base and forming on the planar surface of the transparent base a diffusion-preventing mask with respective substantially circular apertures of smaller diameter than the diameters of the respective gradient index lenses to be formed along the surface of the base, the apertures being centered on the optical axes of the respective lenses to be formed, the apertures each having a diameter rm extending perpendicular to the respective axis and parallel to the respective diametral width such that a ratio a/rm for each aperture satisfies a relation 1.75<a/rm<4.5;   b) diffusing ions of a doping substance which increases by ion exchange the refractive index of the transparent base into the transparent base through the apertures in the mask to a depth sufficient to form said gradient index lenses; and   c) thereafter removing the mask from the transparent base and thereby making said plate microlens.